A continuing problem in the field of communications is the ability to test the systems in order to improve their maintainability. In current testing, one or more of the elements of the communication system is replaced with a substitute testing device. While this permits portions of the system to be tested, the testing device eliminates an important element, such as the decoder, from the system. Since errors can result from the interaction of various elements of the system, the testing is incomplete unless all of the system elements are present during the testing.